Recent growing international interest in reduction of CO2 emission regarded as causative agent of global warming has given a boost to technological innovation for transition from the energy resource that emits a large quantity of CO2 to the next generation energy realized by reusing natural energy and thermal energy. Possible candidates for realizing the next generation energy technology include the one by the use of natural energy such as sunlight and wind power, and the one of reusing the loss of the primary energy such as heat and vibration, resulting from the resource energy emission.
The conventional resource energy has been of concentrated type mainly generated by the large-scale power generation facility. On the contrary, the next generation energy including both natural energy and reusable energy takes unevenly distributed form. In the recent energy utilization, the energy is emitted in the form of exhaust heat without being used, which accounts for approximately 60% of the primary energy. Accordingly, it has been demanded to increase the rate of the next generation energy to the primary energy, and simultaneously, to improve the energy reuse technology, especially, the technology for converting the exhaust heat energy into power.
Considering utilization of the exhaust heat energy which occurs in every possible circumstance, the highly versatile power generation system from the aspect of installation is necessary. The thermoelectric conversion module is one of the strong candidate technologies for the aforementioned system.
The thermoelectric conversion module is a backbone of the thermoelectric conversion technology. The thermoelectric conversion module installed adjacent to the heat source generates power by the temperature difference which occurs in the module. The thermoelectric conversion module is configured to alternately arrange n-type thermoelectric conversion material for generating electromotive force directed from the high-temperature side to the low-temperature side with respect to the temperature gradient, and p-type thermoelectric conversion material having the electromotive force directed opposite the n-type thermoelectric conversion material.
The maximum output P of the thermoelectric conversion module is determined by a product of a heat flow Q into the module and a conversion efficiency n of the thermoelectric conversion material. The heat flow Q depends on the module structure suitable for the thermoelectric conversion material. The conversion efficiency η depends on the dimensionless variable ZT determined by Seebeck coefficient S, resistivity ρ, and the thermal conductivity κ of the material. It is therefore necessary to improve the physical property of the thermoelectric conversion material in order to improve the conversion efficiency.
Various studies have been made concerning the thermoelectric conversion material for solving the aforementioned problem. The BiTe alloy is one of the thermoelectric conversion materials which have been put into practical use. The materials of both Bi and Te exhibit high conversion efficiency but are costly. As the Te exhibits significantly high toxicity, it is difficult to realize the mass production, cost reduction and environmental load reduction. The high efficiency thermoelectric conversion material which replaces the BiTe alloy has been demanded. The following Patent Literature 1 discloses the thermoelectric conversion material derived from the material that includes Heusler alloy type crystal structure.